#define _CRT_SECURE_NO_WARNINGS 1
#include<stdio.h>
int main()
{
	int i = 0;
	double sum = 0.0;
	for (i = 1; i <= 100; i++)
	{
		if(i%2==0)
		{
			sum -= 1.0 / i;
		}
		else
			sum += 1.0 / i;

	}
	printf("%f", sum);

	return 0;
}